lkml.org 
[lkml]   [2006]   [Aug]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8


On Mon, 7 Aug 2006, Bill Huey wrote:

> On Mon, Aug 07, 2006 at 07:56:15PM -0700, Bill Huey wrote:
>> On Thu, Aug 03, 2006 at 10:27:41AM -0400, Steven Rostedt wrote:
>>
>> ...(output and commentary a log deleted)...
>>
>>> This could also have a side effect that messes things up.
>>>
>>> Unfortunately, right now I'm assigned to other tasks and I cant spend
>>> much more time on this at the moment. So hopefully, Ingo, Thomas or
>>> Bill, or someone else can help you find the reason for this problem.
>>
>> Steve and company,
>>
>> Speaking of which, after talking to Steve about this and confirming this
>> with a revert of changes. put_task_struct() can't deallocated memory from
>> either the zone or SLAB cache without taking a sleeping lock. It can't
>> be called directly from finish_task_switch to reap the thread because of
>> that (violation in atomic).
>>
>> It is for this reason the RCU call back to delay processing was put into
>> place to reap threads and was, seemingly by accident, missing from
>> patch-2.6.17-rt7 to -rt8. That is what broke it in the first place.
>>
>> I tested it with a "make -j4" which triggers the warning and it they all
>> go away now.
>>
>> Reverse patch attached:
>
> Resend with instrumentation code removed:
>
> bill
>
>

I had a long discussion with Paul McKenney about this. I opposed the patch
from a latency point of view: Suddenly a high-priority RT task could be
made into releasing a task_struct. It would be better for latencies to
defer it to a low priority task.

The conclusion we ended up with was that it is not a job for the RCU
system, but it ought to be deferred to some other low priority task to
free the task_struct.

Esben

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-08-10 00:09    [W:2.927 / U:9.528 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site